Industrial abrasive tools typically include abrasive grains of a hard substance affixed to a rigid core. The core can be adapted to be manually or power driven in moving contact with a work piece to grind, cut, polish or otherwise abrade the work piece to a desired shape. The abrasive grains are usually attached to the core by a material sometimes called a bond.
The cutting ability of abrasive tools generally diminishes with continued use. Ultimately, a tool wears out completely so as to become altogether ineffective for further use. At such time, the worn tool should be replaced with a fresh one. Often the reduced cutting ability is due to causes such as excessive dulling and loss of the abrasive grit. The grit can be lost when the bond wears away or fractures through contact with the work piece. In many cases, only the abrasive and bond are affected by wear and the core remains substantially intact.
The need to replace worn out abrasive tools is important in certain applications such as construction material grinding and cutting. The materials being cut typically include metals, natural stone, granite, concrete and ceramics. These materials tend to wear out tools relatively quickly, and even the most durable abrasive tools which incorporate superabrasive grits, such as diamond and cubic boron nitride ("CBN"). Additionally, construction material abrasive tools are frequently quite large. Abrasive wheels of up to several feet in diameter for cutting asphalt, concrete and other roadway materials are not uncommon. The cost of replacing such tools can be quite high.
To reduce replacement cost, it is usually possible to recondition the core recovered from a worn out tool. This is generally accomplished by removing any residual bond and grit on the core, repairing insubstantial structural defects in the core and applying a new cutting surface of abrasive grit and bond. Removal of bond and grit from recovered abrasive tools is sometimes referred to as stripping.
Many techniques such as scouring and heating also may be used to strip recovered cores. Abrasive tools which employ a metal bond are usually stripped by a combination of chemical and electrochemical processes. That is, the tool is immersed in a chemical bath which is selectively corrosive to the composition of the bond. A suitable electrical voltage may be applied in a manner which further strips the bond from the core by reverse electroplating.
While significant for many abrasive tool types, the ability to strip the core is particularly important in the development of bonds for so-called Metal Single Layer ("MSL") type tools. MSL tools basically are made by applying a thin coating of a bonding material brazing paste to the cutting surface of the core. Grit particles are usually either placed individually or sprinkled on the paste. Finally, the paste is brazed by heat treatment to form a metal alloy bond.
Nickel has been used in traditional bonds for electroplated tools and it can be readily stripped from the core. However, a nickel plated bond is not very suitable for MSL tools because such bond generally needs to be plated onto the core with a plating bath. Plating baths use large volumes of abrasive grit dispersed in the plating liquid. In high performance applications, the grit is frequently diamond or CBN which causes the plating bath to be excessively expensive to maintain. Alternatively, nickel-based bonds can be brazed, but at very high temperatures, typically well above 1000.degree. C. Those temperatures can cause diamond to graphitize and even to distort the sometimes thin cross-sectioned, metal core.
Alloys which include titanium have gained popularity in the field of bonds for MSL tools. Wesgo, Inc. of Belmont, Calif. offers a bond based on copper-silver eutectic with 4.5 wt % titanium under the tradename Ticusil.RTM.. Although this product provides an easily stripped bond, it is relatively expensive due to the silver content, and its performance in service is moderate.
A preferred titanium-containing MSL bond alloy has the composition 70Cu/21Sn/9Ti (wt %). Unfortunately, such bond is not readily strippable by chemical and electrochemical methods. Cu/Sn/Ti-containing bond compositions are thought to strip poorly because (a) tin-bearing intermetallic phases within the bond are resistant to corrosion by stripping chemicals, and (b) a Ti/Fe/Cu/Sn intermetallic phase is formed which strongly adheres the bond to the core. Tin and titanium are melting point depressants for the alloy and titanium reacts with carbon which beneficially causes the molten bond to wet diamond grit during brazing. Therefore, simply reducing the amount of tin and titanium in the composition to improve stripping ability is not acceptable.
A Cu/Sn/Ti bond for brazing superabrasive grit to an MSL abrasive tool is highly desirable. Accordingly, the present invention provides a removable bond for a predominantly iron core abrasive tool comprising a bond composition consisting essentially of
(a) about 62-92 wt % bronze alloy powder containing about 10-30 wt % tin; PA1 (b) about 5-25 wt % copper powder; and PA1 (c) about 3-12 wt % titanium; PA1 (1) mixing to a uniform dispersion, a powder of bronze alloy consisting essentially of about 10-30 wt % tin and a complementary amount of copper; a powder of titanium hydride; and a copper powder in proportions effective to obtain a bond composition consisting essentially of PA1 (2) heating the bond composition to a bronze melting temperature not exceeding about 880.degree. C.; PA1 (3) holding the bond composition at the bronze melting temperature for a melting duration effective to completely liquefy the bronze alloy and titanium hydride; PA1 (4) raising the temperature to a copper dissolution temperature of at least about 900.degree. C.; and PA1 (5) holding the bond composition at the copper dissolution temperature for a dissolving duration effective to substantially completely dissolve the copper powder in the copper-rich alloy phase. PA1 (1) coating a cutting surface of a predominantly iron core of the abrasive tool with an about 10-200 .mu.m thick barrier layer of copper; PA1 (2) mixing to a uniform dispersion PA1 (3) coating the barrier layer with a layer of the paste; PA1 (4) depositing a substantially single layer of abrasive grains on the paste; and PA1 (5) heating the bond composition to a temperature effective to braze the abrasive grains to the abrasive tool.
wherein the bond is substantially free of voids and exists as a mixture consisting essentially of a copper-rich alloy phase and a copper/tin/titanium intermetallic phase.
This invention additionally provides a process for making a removable bond for a predominantly iron core abrasive tool comprising the steps of:
(a) about 70-90 wt % copper; PA2 (b) about 15-21 wt % tin; and PA2 (c) about 3-12 wt % titanium; PA2 (A) a bond composition comprising copper, tin and titanium; and PA2 (B) an effective amount of a liquid binder to form a paste
Still further the present invention provides a process for making a metal single layer abrasive tool which incorporates the novel bond.
There is also provided a metal single layer abrasive tool which incorporates the novel bond. Also according to the present invention there is provided a metal single layer abrasive tool which includes an about 10-200 .mu.m thick barrier layer of copper between the core and a bond composition containing copper, tin and titanium. The present invention additionally provides a process for making a metal single layer abrasive tool comprising the steps of: